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Preconditioning for fast charging, worth it?

SageBrush

REJECT Fascism
May 7, 2015
14,147
19,618
New Mexico
I've read before that Tesla packs have internal resistance in the 30 - 50 mΩ range. Here is a thread for an 100 kWh pack..

So starting from 50 mΩ and 50 kW charging:
Current is 50,000/360 = 140 Amps,
Then resistance losses = 140*140*50/1,000,000 - 0.98 kW

This arithmetic suggests a savings of about a dime per charge if pre-conditioning is avoided. It is actually less, because the higher power curve seen in the beginning of the charging cycle by the pre-conditioned car will result in more resistance losses and therefore less time spinning the motors. This is true because the pre-conditioning only heats up the battery part way.

Pre-conditioning is genius. If the CCS network was not such a tower of Babel, all EVs would have it by now.
 
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Here's an example. past weekend we were low so searched for superchargers. One turned out to be around the corner from where i was (didn't know the area well) @ WaWa. Didn't get a chance to 'precondition'. 250kW supercharger maxed out at 72kW. Lef it after a few minutes to go to a far away supercharger (about 20 miles away) on my route. Same 250kW supercharger -- maxed out at 127kW. So preconditioning matters.
 

avs007

Active Member
May 14, 2021
1,374
1,259
PacNW
Yes preconditioning makes a big difference, just look at Bjorn's many videos on charging, cold tests, races, etc. Take the Taycan for example. Supposed to be able to charge super fast at 270kw, etc. But when the battery is cold, it charged slow as molasses. He calls it cold-gating, when the car will limit charging speeds when the battery is too cold... Converting the numbers, he found most of the cars, will cold gate, if the battery is < 77 degrees F. For the Tesla Model 3, he said the car will run the "after burners" to heat the battery up to 116 degrees while fast charging. So when he did charging tests, the fastest/max speeds were achieved, when the battery temp was > 95 F.

I know I've seen his many races, where when the battery is < 77 degrees, many of the EVs would not take any more than 80kw, but if the battery was > 95 degrees at the same SoC, it would take > 150kw.
 

Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
7,992
16,111
La Conner, WA
Everyone agrees that pre-conditioning certainly can make supercharging run faster.

The debate was if it was overall more efficient. Does using a few KWH to heat the battery pay for itself with increased charging efficiency, or would you be better off without preconditioning assuming money is more important than charging time.

If money is more important than charging speed/time, then yes, it would behoove you to avoid preconditioning. Preconditioning uses several kWh, which is roughly valued at a buck or two per charging session, depending on temperature and how many charges you do in a day (the first charging session will use the most energy).
 

avs007

Active Member
May 14, 2021
1,374
1,259
PacNW
Everyone agrees that pre-conditioning certainly can make supercharging run faster.

The debate was if it was overall more efficient. Does using a few KWH to heat the battery pay for itself with increased charging efficiency, or would you be better off without preconditioning assuming money is more important than charging time.
From what I've seen on Bjorn's videos, preconditioning the battery can draw around 6kw. Assuming worst case the car tries to preheat the battery for an hour before you arrive, (which according to the owners manual, says preheating the battery could take up to an hour), that means it would cost you on average < $2.00 given the average price of supercharging of 34 cents/kw. And that's if it's heating the battery full tilt for an hour, which it usually won't. I don't know about you, but I'm not going to sweat $2.00 And that is if you pay the supercharger rate for those 6kw... If I precondition at home, those same 6kw will cost me 42 cents. I'm not going to lose any sleep over 42 cents...
 
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From what I've seen on Bjorn's videos, preconditioning the battery can draw around 6kw. Assuming worst case the car tries to preheat the battery for an hour before you arrive, (which according to the owners manual, says preheating the battery could take up to an hour), that means it would cost you on average < $2.00 given the average price of supercharging of 34 cents/kw. And that's if it's heating the battery full tilt for an hour, which it usually won't. I don't know about you, but I'm not going to sweat $2.00 And that is if you pay the supercharger rate for those 6kw... If I precondition at home, those same 6kw will cost me 42 cents. I'm not going to lose any sleep over 42 cents...

I agree it's not a lot of money - a dollar or so for a more typical pre-heat use case.

But it's interesting to know if you're getting anything other than faster-peak-charging-speed for that dollar.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
7,992
16,111
La Conner, WA
I'd assume charging rates all converge towards the end of the session - the big win is the early peak rate in my experience. As you fill towards the top, it slows down regardless of conditioning

Sure, but area under the curve is important. If you can charge three or four times as fast from 0-60%, your overall charging session is going to be significantly shorter, even if you charge up to 100%, which is pretty rare.
 
Everyone agrees that pre-conditioning certainly can make supercharging run faster.

The debate was if it was overall more efficient. Does using a few KWH to heat the battery pay for itself with increased charging efficiency, or would you be better off without preconditioning assuming money is more important than charging time.
Actually, as the original poster on this, my question was not really about money (though certainly a valid question).

My original question was whether the time saved charging through preconditioning was or could be offset by the extra Time needed to charge the battery since the preconditioning clearly drained the battery on the way to the Supercharger? In certain cases, especially when quite cold out, the preconditioning can begin many miles from the charger and the drain, in my mind, was quite significant.

Simply put, the “preconditioned” battery starts out at a lower percentage merely because it has been preconditioned. Does the quicker pace of charging offset this lower starting point?
 
If you are an hour away it doesn't do anything initially in my experience. And if you are that far away it probably doesn't need to precondition for faster charging that much any way. Battery will naturally warm.

I deliberately never use it (added separate Saved GPS locations for landmarks near Super Chargers). Since all it does is waste energy.

I also prefer not charge my battery at 250kw. 125kw-ish is just fine by me.
If we assume Tesla's algorithm is a decent one (and Tesla does seem to put a lot more thought into its fast charging algorithm than any other EV company), wouldn't it be just as hard or perhaps harder on the battery to try to charge it at an improper temperature than it would be to allow the car to do its thing before you arrive? Formation of dendrites and other undesirable stuff in your battery is a function of a lot of factors, and temperature during fast charging is a big one.
 

avs007

Active Member
May 14, 2021
1,374
1,259
PacNW
Actually, as the original poster on this, my question was not really about money (though certainly a valid question).

My original question was whether the time saved charging through preconditioning was or could be offset by the extra Time needed to charge the battery since the preconditioning clearly drained the battery on the way to the Supercharger? In certain cases, especially when quite cold out, the preconditioning can begin many miles from the charger and the drain, in my mind, was quite significant.

Simply put, the “preconditioned” battery starts out at a lower percentage merely because it has been preconditioned. Does the quicker pace of charging offset this lower starting point?
I don't think you would ever really lose anything by preconditioning... On one of my previous roadtrips, I was comparing the difference between leaving home with 80% vs 100%... What I've found was, that when arriving at the SC with 18%, adding 20% only took 5 minutes.... Preheating the battery is not going to drain 20% of your battery. From what I've read, preconditioning only uses between 6-11kw. That means even at the worst, it would only drain like 10% over an hour, means you would only lose a few minutes at most of charging time.
 
PRO TIP: I found clicking on the Text/Banner “Pre-conditioning Battery” just above your next navigation step cancels the Pre-Conditioning. No need to route to a nearby location like earlier suggestions offered.

I just returned from a decent road trip with the family, 800+ miles in around 20 deg weather. I found myself canceling Pre-Conditioning Each time. I noticed a 100 kw/m spike once Pre-Condition kicked on. I preferred to arrive with a few extra miles buffer rather than faster charging. This was just my range anxiety showing, not cost savings. I suppose in the future i will try to place full trust in the system and see where it takes me. However I feel the miles lost in cold weather are significant enough to make me want to save every little bit I can just in case.
 
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mswlogo

Well-Known Member
Aug 27, 2018
8,427
7,959
MA, NH
If we assume Tesla's algorithm is a decent one (and Tesla does seem to put a lot more thought into its fast charging algorithm than any other EV company), wouldn't it be just as hard or perhaps harder on the battery to try to charge it at an improper temperature than it would be to allow the car to do its thing before you arrive? Formation of dendrites and other undesirable stuff in your battery is a function of a lot of factors, and temperature during fast charging is a big one.
Possibly ;) But I think it just slows things down to protect the battery. Just like it would on a cold charge at home, which happens all the time. It’s probably at ideal temp at the start with precondition. But by the end it’s probably working to keep things cool. Especially an a hot day.

Both my Model 3 (one year 10K miles) and Model X (2.5 years 27K) had absurdly low degradation vs what I’ve seen many posted here (on the order of single digits counted on 1 hand).

Absolutely no proof my methods mattered or are valid. But I’ll keep doing it. Normal practice is never over 80%, unless I can drive it immediately. And make sure I do charge to 100% occasionally.
 

Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
7,992
16,111
La Conner, WA
PRO TIP: I found clicking on the Text/Banner “Pre-conditioning Battery” just above your next navigation step cancels the Pre-Conditioning. No need to route to a nearby location like earlier suggestions offered.

I just returned from a decent road trip with the family, 800+ miles in around 20 deg weather. I found myself canceling Pre-Conditioning Each time. I noticed a 100 kw/m spike once Pre-Condition kicked on. I preferred to arrive with a few extra miles buffer rather than faster charging. This was just my range anxiety showing, not cost savings. I suppose in the future i will try to place full trust in the system and see where it takes me. However I feel the miles lost in cold weather are significant enough to make me want to save every little bit I can just in case.

In my experience, tapping the banner just hides it - preconditioning continues to happen.
 
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Possibly ;) But I think it just slows things down to protect the battery. Just like it would on a cold charge at home, which happens all the time.
Yeah but home charging doesn't stress the battery because it maxes out at around 12kW. It's likely that Tesla tries to keep degradation constant and if the battery is cold, it has to throttle charge rate to avoid increasing degradation.
It’s probably at ideal temp at the start with precondition. But by the end it’s probably working to keep things cool. Especially an a hot day.
I wouldn't expect that much difference in charge time on a hot day. It's likely very cold charging that does the most damage to the battery.
 

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